Natural intestines of animals such as sheep, pig, cow and the like have been conventionally used as a casing for sausages, etc. However, these natural intestine casings have drawbacks in that they are generally not crisp and are too hard to be chewed completely, and as a result debris of such casing which is a piece of intestine is left in the mouth.
As a method for improving such drawbacks of the natural intestines, a method for tenderizing an edible casing for sausages treated with soy sauce (see, JP-A-1989-199537), a modified natural animal intestine modified by immersing in an aqueous solution of transglutaminase (see, JP-A-1997-117252), and a method for producing a sausage having a crisp and tender natural intestine casing, which comprises packing meat paste for sausage into a natural intestine casing, treating the packed meat paste with warm water adjusted to acidity of pH 2 to 5 or alkalinity of pH 8 to 10, and then heat-treating by the conventional method (see, JP-A-1996-242817).
At the present time, however, it is still difficult to say that the above drawbacks have been completely solved even if those methods as mentioned above are adopted. Therefore, there is a desire for a method for producing natural intestines used for sausage casing improved in the texture and hardness.